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Abstract

Laser speckle contrast imaging has become a widely used tool for dynamic imaging of blood flow, both in animal models and in the clinic. Typically, laser speckle contrast imaging is performed using scientific-grade instrumentation. However, due to recent advances in camera technology, these expensive components may not be necessary to produce accurate images. In this paper, we demonstrate that a consumer-grade webcam can be used to visualize changes in flow, both in a microfluidic flow phantom and in vivo in a mouse model. A two-camera setup was used to simultaneously image with a high performance monochrome CCD camera and the webcam for direct comparison. The webcam was also tested with inexpensive aspheric lenses and a laser pointer for a complete low-cost, compact setup ($90, 5.6 cm length, 25 g). The CCD and webcam showed excellent agreement with the two-camera setup, and the inexpensive setup was used to image dynamic blood flow changes before and after a targeted cerebral occlusion.

Figures (7)

(A) Schematic of the two-camera setup for simultaneous laser speckle imaging with a CCD camera and a webcam using traditional optics and illumination components. A 50-50 beamsplitter separates the light between the two imaging arms. (B) Schematic of the low-cost, compact laser speckle imaging system, where the lenses are inexpensive aspheres and the illumination is a laser pointer. In both (A) and (B), the 532 nm laser is only used for the animal study. (C) and (D) illustrate the two different samples assessed in this study. (C) A microfluidic flow phantom is used for in vitro validation and different flow levels are controlled using a syringe pump. (D) In vivo validation is performed using a mouse prepared with bi-lateral cranial windows for assessment of setup (A) and (B), respectively.

Representative speckle contrast images averaged over 10 frames illustrating the location of the ROIs used for analysis (shown in red for color mode and in blue for Bayer mode and CCD images). Speckle contrast images are shown for (A) the webcam acquired in color mode within the two-camera setup (mean K = 0.0536), (B) the webcam acquired in Bayer mode within the two-camera setup (mean K = 0.132), (C) the CCD camera acquired simultaneously with the webcam in Bayer mode (mean K = 0.167), (D) the webcam acquired in color mode in the inexpensive setup (mean K = 0.0676), and (E) the webcam acquired in Bayer mode in the inexpensive setup (mean K = 0.167). The color bar for (D) is the same as that for (A), and the color bar for (E) is the same as that for (B) and (C). Scale bars = 0.5 mm. (F) Cropped profiles are shown for images (A-E). Each profile is averaged over 20 pixels, and is plotted in physical space (mm) with the channel locations lined up for clarity.

Scatter plots illustrating the relative flow changes between different speeds of the microfluidic experiment, with a direct comparison between the CCD camera and the webcam in (A), and the webcam in the inexpensive setup vs. the two-camera setup in (B). Speed 2 was used for the baseline flow in (A), and speed 3 was used for the baseline flow in (B). Each point is the average relative flow with error bars in each direction depicting the standard deviations for each camera or setup.

Results from the two-camera in vivo experiment, showing registered baseline speckle contrast images for the CCD camera (A) and the webcam (B) with ROI locations used for analysis. Color bars indicate the range of speckle contrast values (K) displayed in the images. Scale bars = 0.5 mm. The plots in (C) and (D) show the time courses for the vessel and parenchyma ROIs, respectively, and show the CCD and webcam (WC) relative flows for each ROI on the same plot for direct comparison. The colors of the ROIs in (A) and (B) match the colors used for the plots in (C) and (D), and the break in the time course was when the green laser was left on continuously for clot formation.

Relative blood flow overlay from the two-camera in vivo experiment depicting the reduction in flow after the stroke overlaid over baseline speckle contrast images with a 35% reduction of baseline cutoff for the CCD camera (A) and the webcam (B). Targeted area for photothrombosis is marked with a green circle in each image. Scale bars = 0.5 mm.

Results from the inexpensive in vivo experiment, showing baseline speckle contrast images from the webcam with ROI locations used for analysis (A). Color bar indicates the range of speckle contrast values (K) displayed in the image. (B) Relative blood flow overlay depicting the reduction in flow after the stroke overlaid over baseline speckle contrast images with a 35% reduction of baseline cutoff. Targeted area for photothrombosis is marked with a green circle. Scale bars = 0.5 mm. The plots in (C) and (D) show the relative flow time courses for the ROIs split onto two plots for visualization. The colors of the ROIs in (A) match the colors used for the plots in (C) and (D), and the break in the time course was when the green laser was left on continuously for clot formation.